1. Field of the Invention
The present invention relates to a butadiene-based copolymer, more particularly relates to an alkyl acrylate-butadiene-aromatic vinyl compound copolymer with a specific functional group. Such a copolymer is suitable as an impact modifier for a PC/PBT alloy.
2. Description of the Prior Art
Polycarbonate/polybutylene terephthalate (PC/PBT) alloy has the properties of easy processability, good size stability, heat resistance, solvent resistance and is primarily applied in shaped articles for automobiles and outdoor sports equipment. However, PC/PBT alloy has the problems of being brittle, i.e., having low impact strength at room temperature and low temperatures.
The main measure to improve the physical properties of a PC/PBT alloy is to incorporate some modifiers such as impact modifiers, compatibilizers, glass fiber or fillers. An impact modifier is the most effective one.
There are various types of impact modifiers, including methyl methacrylate-butadiene-styrene (MBS) copolymer, acrylics, chlorinated polyethylene (CPE), ethylene vinyl acetate (EVA) copolymer and acrylonitrile-butadiene-styrene (ABS) copolymer. Among these, MBS impact modifiers most readily display an impact modifying effect at room temperature and low temperatures.
For example, Chacko et al. in U.S. Pat. No. 4,677,150 disclose an MBS modified PC/PBT alloy. The MBS is present in an amount of 20 wt. %, and the resulting alloy is determined to have an impact strength of 25.2 ft-lb/in at room temperature and 2.4 ft-lb/in at -20.degree. C. It reveals that in order to make PC/PBT alloy impart acceptable impact strength at room temperature and low temperatures, a large amount of the conventional MBS, up to 20 wt. % of the total composition, must be added. The reason why the conventional MBS is effective only when the added amount is large is probably because the conventional MBS has no suitable interaction between the interface of the MBS and the PC/PBT alloy, therefore, the MBS is dispersed in the rubber in an uneven manner, that is, the compatibility of the conventional MBS with the alloy is poor. Consequently, the impact modifying effect of the conventional MBS is limited. Furthermore, such a large amount of MBS adversely affects some physical properties such as heat distortion temperature.